Versatile method and system for single mode VCSELs

ABSTRACT

A system and method for providing a single mode VCSEL (vertical cavity surface emitting laser). A lower mirror is formed on a substrate. An active region including one or more quantum wells is formed over the lower mirror. The upper mirror formed over the active region can include multiple layers and may be formed to be have substantially isotropic conductivity. The layers in the upper mirror can include a lightly doped DBR layer, a heavily doped second layer including an isolation region, and a third heavily doped DBR layer. The active region may include conduction layers, which may be periodically doped, to improve conductivity and reduce free carrier absorption.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.09/724,820 filed Nov. 28, 2000 now U.S. Pat. No. 6,905,900.

TECHNICAL FIELD OF THE INVENTION

The present invention relates, in general, to semiconductor lasers and,in particular, to a versatile system for producing single transversemode Vertical-Cavity Surface-Emitting Lasers (VCSELs).

BACKGROUND OF THE INVENTION

The Vertical Cavity Surface Emitting Laser (VCSEL) is rapidly becoming aworkhorse technology for semiconductor optoelectronics. VCSELs cantypically be used as light emission sources anywhere other laser sources(e.g., edge emitting lasers) are used, and provide a number ofadvantages to system designers. Hence, VCSELs are emerging as the lightsource of choice for modern high-speed, short-wavelength communicationsystems and other high-volume applications such as optical encoders,reflective/transmissive sensors and optical read/write applications.

Surface-emitting lasers emit radiation perpendicular to thesemiconductor substrate plane, from the top or bottom of the die. AVCSEL is a surface-emitting laser having mirrors disposed parallel tothe wafer surfaces that form and enclose an optical cavity between them.VCSELs usually have a substrate upon which a first mirror stack andsecond mirror stack are disposed, with a quantum well active regiontherebetween. Gain per pass is much lower with a VCSEL than anedge-emitting laser, which necessitates better mirror reflectivity. Forthis reason, the mirror stacks in a VCSEL typically comprise a pluralityof Distributed Bragg Reflector (DBR) mirrors, which may have areflectivity of 99% or higher. An electrical contact is usuallypositioned on the second mirror stack, and another contact is providedat the opposite end in contact with the substrate. When an electricalcurrent is induced to flow between the two contacts, lasing is inducedfrom the active region and emits through either the top or bottomsurface of the VCSEL.

VCSELs may be broadly categorized into multi-transverse mode andsingle-transverse mode, each category being advantageous in differentcircumstances. A goal in manufacturing single-mode VCSELs is to assumesingle-mode behavior over all operating conditions, without compromisingother performance characteristics. Generally, the active regions ofsingle transverse mode VCSELs require small lateral dimensions, whichtend to increase the series resistance and beam divergence angle.Furthermore, a device that is single-mode at one operating condition canbecome multi-mode at another operating condition, an effect thatdramatically increases the spectral width and the beam divergence of theemitted radiation of the VCSEL.

Depending upon the application, the output mode of a VCSEL can eitherpositively or negatively affect its use in signal transmission and otherapplications. The mode structure is important because different modescan couple differently to a transmission medium (e.g., optical fiber).Additionally, different modes may have different threshold currents, andcan also exhibit different rise and fall times. Variation in thresholdcurrents, which can be caused by different modes, combined withdifferent coupling efficiencies of different modes can cause couplinginto a transmission medium to vary in a highly non-linear manner withrespect to current. Variable coupling to a transmission medium, combinedwith different rise and fall times of the various modes, can causesignal pulse shapes to vary depending on particular characteristics ofthe coupling. This can present problems in signal communicationsapplications where transmission depends on a consistent and reliablesignal. Other applications (e.g., printing devices, analyticalequipment) may require a consistent and focused light source or spectralpurity characteristics that render multiple mode sources inefficient orunusable.

Manufacturing a VCSEL with mode control and high performancecharacteristics poses a number of challenges. It is difficult tomanufacture VCSELs that efficiently operate in the lower order mode(single mode). Most conventional VCSELs tend to lase in higher-ordertransverse modes, whereas single transverse mode lasing is preferred forsome applications, such as sensors. Conventional attempts to produce asingle mode VCSEL have generally resulted in structures having outputpower insufficient for practical use in most applications, as theyremain single mode only over small current ranges. Usually, tomanufacture a VCSEL, a relatively large current aperture size isrequired to achieve a low series resistance and high power output. Aproblem with a large current aperture is that higher order lasing modesare introduced so that single mode lasing only occurs just abovethreshold, if at all. Manufacturing a VCSEL with a smaller currentaperture to obtain single mode behavior causes multiple problems: theseries resistance becomes large, the beam divergence angle becomeslarge, and the attainable power becomes small. Some conventionalanti-guide structures may achieve this but suffer from manufacturingdifficulties, particularly in requiring an interruption in epitaxialgrowth, a patterning step, and subsequent additional epitaxy. Otherlarge single mode VCSELs require multi-step MBE or MBE/MOCVDcombinations to manufacture, creating alignment and yield problems;increasing production costs and reducing commercial viability.

BRIEF SUMMARY OF THE INVENTION

The following summary of the invention is provided to facilitate anunderstanding of some of the innovative features unique to the presentinvention, and is not intended to be a full description. A fullappreciation of the various aspects of the invention can be gained bytaking the entire specification, claims, drawings, and abstract as awhole.

Therefore, a versatile system for producing a single mode VCSEL in acost-effective and efficient manner, sustaining single mode operationover all current ranges is now needed, providing commercially viableVCSEL power output and performance while overcoming the aforementionedlimitations of conventional methods.

In the present invention, electrical, thermal, and geometric opticalproperties of VCSEL components are designed and selected to providecurrent peaking in the center of a VCSEL device, coincident with thepeak of the lowest order mode and to maximize loss in, or eliminatecompletely, higher order modes. Optionally, other mode controltechniques can be used in conjunction with the teachings of the presentinvention to optically tailor the loss profile to prefer the fundamentalmode.

The present invention provides structures and methods for producing asingle mode VCSEL comprising a substrate, a bottom contact portiondisposed upon a lower surface of the substrate, a lower mirror portiondisposed upon an upper surface of the substrate, an active regiondisposed upon the lower mirror portion, and a current spreading uppermirror portion formed from electrically isotropic material and disposedupon the active region, an equipotential portion, which can include anadditional mirror, disposed upon the upper current spreading mirrorportion, an insulating layer interposed between the upper currentspreading mirror portion and the equipotential portion and adapted toform an aperture therebetween, and an upper contact portion disposedupon the equipotential layer outside the perimeter of the aperture.

The present invention provides a VCSEL component adapted to providedsingle mode operation over wide current ranges, comprising asemiconductor substrate having a lower surface and an upper surface, abottom electrical contact disposed along the lower surface of thesemiconductor substrate, a lower mirror formed of n-type material anddisposed upon the upper surface of the semiconductor substrate, anactive region having a plurality of quantum wells disposed upon thelower mirror portion, an upper current spreading mirror formed fromelectrically isotropic material and disposed upon the active region, anequipotential layer, which can include another mirror, disposed upon theupper mirror portion, a first upper electrical contact disposed upon theequipotential layer at a first lateral end of the VCSEL component, asecond upper electrical contact disposed upon the equipotential layer ata second end of the VCSEL component at a particular distance from thefirst upper electrical contact, a first isolation region disposedbeneath the first upper contact and traversing the equipotential layer,the upper mirror, the active region, and the lower mirror, a secondisolation region disposed beneath the second upper contact andtraversing the equipotential layer, the upper mirror, the active region,and the lower mirror, and an insulating layer interposed between theupper mirror and the equipotential layer and adapted to formtherebetween an aperture.

The present invention further provides a method of providing antiguidemode selectivity in a VCSEL, including the forming of a VCSEL structurehaving a substrate, a bottom contact portion disposed upon a lowersurface of the substrate, a lower mirror portion disposed upon an uppersurface of the substrate, an active region disposed upon the lowermirror portion, and an upper current spreading mirror portion formedfrom electrically isotropic material and disposed upon the activeregion, providing a substantially equipotential layer disposed upon theupper mirror portion, selectively interposing an electrically insulatinglayer between the upper mirror portion and the equipotential layer toform an aperture therebetween, wherein the electrically insulating layeris adapted to provide a greater nominal cavity resonance outside theaperture than inside it, and providing an upper contact portion disposedupon the equipotential layer.

The novel features of the present invention will become apparent tothose of skill in the art upon examination of the following detaileddescription of the invention or can be learned by practice of thepresent invention. It should be understood, however, that the detaileddescription of the invention and the specific examples presented, whileindicating certain embodiments of the present invention, are providedfor illustration purposes only because various changes and modificationswithin the scope of the invention will become apparent to those of skillin the art from the detailed description of the invention and claimsthat follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form part of the specification,further illustrate the present invention and, together with the detaileddescription of the invention, serve to explain the principles of thepresent invention.

FIG. 1 is an illustrative schematic of VCSEL component according to thepresent invention;

FIG. 2 is an illustrative diagram of the operation of the VCSELcomponent in FIG. 1;

FIG. 3 is an illustrative schematic of another VCSEL component accordingto the present invention;

FIG. 4 is an illustrative schematic of VCSEL component according to thepresent invention; and

FIG. 5 is an illustrative diagram of the operation of the VCSELcomponent in FIG. 4.

It should be understood that the drawings are not necessarily to scaleand that the embodiments are illustrated using graphic symbols, phantomlines, diagrammatic representations and fragmentary views. In certaininstances, details which are not necessary for an understanding of thepresent invention or which render other details difficult to perceivemay have been omitted. It should be understood, of course, that theinvention is not necessarily limited to the particular embodimentsillustrated herein.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the presentinvention are discussed in detail below, it should be appreciated thatthe present invention provides many applicable inventive concepts whichcan be embodied in a wide variety of specific contexts. The specificembodiments discussed herein are merely illustrative of specific ways tomake and use the invention and do not delimit the scope of theinvention.

It should be understood that the principles and applications disclosedherein can be applied in a wide range of optoelectronic applications.For purposes of explanation and illustration, the present invention ishereafter described in reference to VCSEL laser sources. However, thesame system might be applied in other applications where a single modesource is utilized.

As previously discussed, one of the limitations of conventional singlemode VCSEL approaches is their tendency to become multi-moded as currentis increased, resulting in a very small effective current range and,hence, minimal power output, for single mode operation. ConventionalVCSELs generally become multi-moded as current is increased because ofcurrent crowding near the edge of the emitting region and the resultingreduction in available gain in the center of the device, which is alsocaused by the sharp peaking of the lowest order mode in the center. Thisis true even for conventional devices having mode control structures.

In contrast, the present invention provides current peaked in the centerof a VCSEL device, coincident with the peak of the fundamental (i.e.,lowest order) mode. Optionally, other mode control techniques can beused in conjunction with the teachings of the present invention tooptically tailor the loss profile to prefer the fundamental mode (e.g.,use of long cavities, top surface patterning).

The present invention thus provides a single mode VCSEL having outputpower sufficient to meet the performance requirements of cost-sensitivecommercial applications. Referring first to FIG. 1, a cross-sectionalview of a VCSEL component 100 in accordance with the present inventionis illustrated. VCSEL 100 comprises a substrate 102, formed of asuitable semiconductor material (e.g., Galium Arsenide [GaAs], IndiumPhosphide [InP], or combinations thereof). VCSEL 100 further comprises abackside contact portion 104, formed of a suitable metallic or otherconductive material, and adjoining a lower surface of substrate 102. Afirst semiconductor mirror stack 106 is disposed along the upper surfaceof substrate 102. Mirror 106 comprises a plurality of mirror pairs ofalternating low and high refractive indexed material (e.g., DBR mirrors)and can be n-doped, for example. Disposed upon an upper surface ofmirror 106 is active region 108. Active region 108 contains a number ofquantum wells (e.g., three GaAs quantum wells). A second semiconductorcurrent spreading mirror stack 110 is disposed along an upper portion ofregion 108 and can include a plurality of mirror pairs of p-dopedmaterial, for example. A conduction layer 112 is disposed atop andadjoining current spreading mirror 110. The resistivity of mirror 110 ismuch higher than in layer 112, and the conductivity of mirror 110 is asisotropic as possible. Layer 112 comprises a very high conductivitylayer (e.g., 4 to 10 times the conductance of mirror 110) on top ofmirror 110, which acts substantially like an equipotential (e.g.,resistivity of about 0.01 ohm/cm). Layer 112 can comprise a highly dopedsemiconductor grown on the lower structures of VCSEL 100 (e.g., AlGaAs).Layer 112 can also comprise or include a DBR mirror structure.Alternatively, layer 112 can comprise a substantially equipotentialportion of mirror 110. Because n-type mirrors typically have anisotropicconduction, it can be preferable to use a p-type material to form mirror110. In VCSEL production processes where tunnel junctions produce nearlyohmic contact between n and p regions, without normal p-n junctioncharacteristics, mirrors 106 and 110 can both be formed of either p-typeor n-type material, as described hereafter in greater detail withreference to FIG. 4.

Generally, when the composition of any of the materials used comprisesmore than two chemical elements, that material's thermal conductivitydecreases significantly. This increases thermal lensing while decreasingmaximum power. It is thus desirable to use binary compositions,especially in proximity to region 108 (i.e., in mirrors 106 and 110).

VCSEL 100 further comprises a first electrical insulation region 114 anda second electrical insulation region 116, interposed between mirror 110and conduction layer 112 in distally separate relation to one another,forming an aperture 118 between mirror 110 and layer 112. Although, asdepicted in the cross sectional view of FIG. 1, regions 114 and 116 areseparate structures, it is important to note that they can includesegments of a single contiguous insulating region having the aperture(e.g., a circular aperture) formed therein. In this embodiment, thereshould be some electrical insulation between layer 112 and mirror 110,except for the area of aperture 118. This confines current flow towardthe center of VCSEL 100. Optionally, regions 114 and 116 can be formedfurther within layer 110 (i.e., not immediately adjacent to layer 112),as described in later reference to FIG. 3. Insulation regions 114 and116 can comprise an oxide, or some other suitable insulator available inthe desired semiconductor process. The insulating regions can be anyinsulating material of any thickness (e.g., Al₂O₃ or air), but isoptimal when reflectance of mirror 110, as measured from region 108, isminimized by the choice of thickness and position of the insulatingregions. This causes more loss for higher order modes. Thus, theinsulation regions can be designed or patterned to increase operationalselectivity toward the fundamental mode. The thickness and positioningof the insulating regions can also be optimized such that the nominalcavity resonance outside the aperture 118 is at a longer wavelength thaninside, providing an antiguide effect. Despite lower real indices ofmaterials such as Al₂O₃, proper thickness and positioning of theinsulating regions will provide an effective higher index and result ina longer resonant wavelength. It is possible that, depending upon theprocesses and materials used, extended insulation areas may emanate fromregions 114 and 116, having different electrical and optical effects onthe performance of VCSEL 100. This phenomenon may be exploited toprovide independent control of the optical and resistive effects, byaltering the composition of the insulation regions (e.g., adding aproton implant to the regions).

VCSEL component 100 further comprises a first upper contact portion 120and a second upper contact portion 122. Contacts 120 and 122 are formedof a suitable metallic or other conductive material atop conductionlayer 112 in distally separate relation to one another, separated by aspan 124. As depicted, regions 114 and 116 are formed beneath, andextending beyond, contacts 120 and 122, respectively, such that aperture118 is smaller than span 124. Alternatively, contacts 120 and 122 andregions 114 and 116 can be formed such that contacts 120 and 122 overlapregions 114 and 116, resulting in an aperture 118 larger than span 124.As shown in FIG. 1, a first isolation region 126 is implanted beneathcontact 120, traversing portions of layer 112, region 114, mirror 110,and region 108, and extending into mirror 106. Similarly, a secondisolation region 128 is implanted beneath contact 122, traversingportions of layer 112, region 116, mirror 110, and region 108, andextending into mirror 106.

The conductivity and sheet conductance of layer 112 are many times(e.g., an order of magnitude) that of mirror 110. Layer 112 is formed ofa thickness sufficient to enhance reflectivity of mirror 110. Thelateral conductance of mirror 110 should be low, such that lateralcurrent spreading is minimized. Mirror 110 and 112 are designed to havea phase relationship such that the combined structures provide maximumreflectivity inside aperture 118. Layer 112 provides mirror reflectivitybecause of its interface with the outside world.

Vertical conductance of mirror 110 should be high enough not to increaseresistance excessively. Because the mirror stack is made ofsemiconductors of different band gaps, the mirror should be designed asisotropically conductive as is reasonable to reduce lateral currentflow. As such, layers which have higher mobilities need lower doping,and layers with lower mobilities need higher doping, so that theresistivity is nearly the same all the way through and independent ofdirection. The product of the hole concentration and the mobility needsto be a constant for as much of mirror 110 as is possible. Theinterfaces between the semiconductors need to be doped more heavily andgraded due to lower mobilities in the intermediate compositions of thegrade and the modulation doping of lower gap material adjacent to widergap material.

By forming an equipotential portion 112, and current spreading mirror110 with the properties described above, and providing thecurrent-restrictive aperture 118 therebetween, the present inventionfocuses the VCSEL current in the center of the device and at the lowestorder mode, while minimizing and dispersing fringe current andeffectively eliminating higher order modes. Mode selectivity is furtherprovided by the antiguide effects of the present invention, as describedabove. FIG. 2 provides an illustration of advantages of the presentinvention. Indicators 200 depict operational current flow of VCSEL 100.The current density is maximized in the center portion 202 of VCSEL 100,coinciding with the peak of the lowest order mode. Current coincidingwith higher order modes is widely dispersed, maximizing loss for thosemodes and effectively damping all but the lowest order mode. The presentinvention thus provides a single mode (i.e. the lowest order mode) VCSELdevice, operational over a wide current range.

As previously indicated, a number of optional measures can beimplemented to further increase modal selectivity in conjunction withthe present inventions. Spacing and thickness of the various componentlayers of VCSEL 100 can be varied to increase spreading effects (i.e.,loss) of current associated with higher order modes (e.g., thickness oflayers 114 and 116 can be increased). Additional structures can be addedto VCSEL 100 to enhance optical selectivity. Referring back to FIG. 1,one such option is depicted in conjunction with VCSEL 100. A dielectricstack mode control structure is disposed atop layer 112. This structurecomprises a first dielectric layer 130, disposed on an upper surface oflayer 112 along span 124, and a second dielectric layer 132, disposedatop layer 130. Layer 132 can be positioned to align with aperture 118.Layer 130 is formed of a suitable material (e.g., SiO₂) with a thicknessequivalent to one fourth (or some multiple thereof) the wavelength oflight sourced by VCSEL 100. Layer 132 is formed of a suitable material(e.g., Si₃N₄) of a thickness, when combined with the thickness of layer130, equivalent to one half (or some multiple thereof the wavelength oflight sourced by VCSEL 100. The effective mirror reflectivity underlayer 130 is reduced and optical loss is increased, except for the areaunder layer 132, where the mirror reflectivity is either unaffected orenhanced, depending upon the material used to form layer 132. Thus,reflection back to the mirror under layer 132 is greater; and larger,higher order modes are suppressed. These effects can be combined withthe other teachings of the present invention to further strengthensingle mode selection and output.

Referring now to FIG. 3, a cross-sectional view of an alternativeembodiment of a VCSEL component 300 in accordance with the presentinvention is illustrated. VCSEL 300 is substantially similar, inmaterials and construction, to VCSEL 100 of FIG. 1, with the exceptionsdetailed hereafter. VCSEL 300 comprises a substrate 302 and a backsidecontact portion 304 adjoining a lower surface of substrate 302. A firstsemiconductor mirror stack 306 is disposed along the upper surface ofsubstrate 302. Disposed upon an upper surface of mirror 306 is activeregion 308. A second semiconductor mirror stack 310 is disposed along anupper portion of region 308, and a conduction layer 312 is disposed atopand adjoining mirror 310. VCSEL 300 further comprises a first electricalinsulation region 314 and a second electrical insulation region 316,medially interposed within mirror 310 between region 308 and conductionlayer 312, in distally separate relation to one another, forming anaperture 318. VCSEL 300 can be so formed as long as peak gain andcurrent density is realized toward the center of VCSEL 300. In thisembodiment, the portion of mirror 310 above regions 314 and 316 (i.e.,that portion directly adjacent to layer 312) should have as low aresistivity as is reasonable based on control constraints and freecarrier absorption constraints.

As previously taught, heating must be prevented. Free carrier absorptioncauses a lot of heating in VCSEL devices. Heating can be minimized byhaving as low a doping at the electric field peaks as possible. I-Rheating can become severe if doping is reduced excessively to reducefree carrier absorption. Keeping this in mind, reference is now made toFIG. 4, which presents an embodiment of the present invention addressingthese concerns and building upon the teachings above.

FIG. 4 depicts a cross-sectional view of an embodiment of a VCSELcomponent 400 in accordance with the present invention. VCSEL 400comprises a substrate 402, formed of a suitable semiconductor material(e.g., Galium Arsenide [GaAs], Indium Phosphide [InP], or combinationsthereof). VCSEL 400 further comprises a first semiconductor mirror stack404 disposed along the upper surface of substrate 402. Mirror 404comprises a plurality of mirror pairs of alternating low and highrefractive indexed material (e.g., DBR mirrors). AlGaAs DBR mirrors,using AlAs as the lower index extreme to improve thermal conductivity,can be utilized. Alternatively, AlInGaAsPSb, lattice matched to InP witha possible extreme composition of InP, can be utilized to improvethermal conductivity. Disposed upon an upper surface of mirror 404 is afirst heat conduction layer 406. Layer 406 comprises asubstrate-appropriate material (e.g., AlAs for GaAs substrates, InP forInP substrates). Layer 406 is periodically doped to maximize doping atminima of electric fields and can be formed with a thickness on theorder of one micron. This periodic doping can comprise doping heavily inthe nulls of the electric field and doping lightly at the peaks of theelectric field. The periodic doping improves conductivity and reducesthe free carrier absorption. Use of uniformly heavy doping generallyreduces series' resistance.

Disposed upon layer 406 is active region 408. Active region 408comprises a lower p-n junction layer 410 disposed upon layer 406, afirst tunnel junction 412 disposed upon layer 410, an upper p-n junctionlayer 414 disposed upon junction 412, and a second tunnel junction 416disposed upon layer 414. Layers 410 and 414 can contain a number ofquantum wells. By using tunnel junctions 412 and 416, a designer canthen utilize n-type material in the mirror and heat conduction layers,providing significant reduction in free carrier absorption for a givenconductivity. Within region 408, this is a particularly effective way toreduce currents and heating effects.

Disposed upon an upper surface of region 408 is a second heat conductionlayer 418. Layer 418 is also isotropically formed as a current spreader.Layer 418 comprises a lightly doped substrate-appropriate material(e.g., AlAs for GaAs substrates, InP for InP substrates).

A second semiconductor mirror stack 420 is disposed above layer 418.Mirror 420 comprises a first upper mirror layer 422, a second uppermirror layer 424, and a third upper mirror layer 426. Layer 422 isformed to be as isotropic as possible and is lightly doped for freecarrier absorption. Layer 422 can be formed to be of a thicknessapproximately equal to 4.5 periods. Layer 422 can comprise a pluralityof mirror pairs of either n-doped or p-doped material, depending uponthe process used, as previously noted. If n-type material is used, layer422 can be formed above layer 424 (not shown). If layer 422 is formed asshown in FIG. 4, layer 418 may be formed with a thickness ofapproximately one micron, for example. If layer 422 is formed abovelayer 424, then layer 418 should be thicker, formed with a thickness ofapproximately 2.6 microns, for example.

VCSEL 400 further comprises a first electrical insulation region 428 anda second electrical insulation region 430, interposed within layer 424in distally separate relation to one another, forming an aperture 432therebetween. The formation of aperture 432 confines current flowtowards the center of VCSEL 400. As previously described, insulationregions 428 and 430 can comprise any appropriate insulating material ofany thickness (e.g., an oxide) provided that they are formed towardminimizing reflectance of mirror 420, as measured from region 408, andalso toward optimizing nominal cavity resonance to provide anantiguiding. Again, it is possible that, depending upon the processesand materials used, extended resistive regions 434 and 436 may emanatefrom regions 428 and 430, respectively, having different electrical andoptical effects on the performance of VCSEL 400. As previously taught,regions 434 and 436 can be manipulated through design to provideindependent optical and resistive control; however, generally, it isdesirable that these regions are confined as narrowly as possible aroundthe immediate area of regions 428 and 430.

Inside aperture 432, current density is higher than anywhere else, as islater illustrated in reference to FIG. 5. This current density causessignificant IR heating, which must be prevented. Thus, layer 424 cancomprise a heavily p-doped type material, or a moderately n-doped typematerial, or any other appropriate material (e.g., n-InP for an InPbased VCSEL) that provides reduced series resistance and heating effectswithin aperture 432. Optionally, tapers 438 can be formed on the ends ofregions 428 and 430, with tips positioned at electric field nulls, toenhance current confinement and mode selectivity. Layer 426 comprises aheavily doped material formed of appropriate thickness (e.g.,approximately 16 periods for AlGaAs material) to optimize resistance andform, in relation to a conduction layer 440, an equipotential.Conduction layer 440 is disposed atop and adjoining mirror 420 and isformed of a very heavily doped material to minimize resistance. Theresistivity of mirror 420 is higher than in layer 440, and theconductivity of mirror 420 is as isotropic as possible. Layer 440comprises a very high conductivity layer on top of mirror 420, whichacts substantially like an equipotential.

VCSEL component 400 further comprises a first upper contact portion 442and a second upper contact portion 444. Contacts 442 and 444 are formedof a suitable metallic or other conductive material atop conductionlayer 440 in distally separate relation to one another, separated by aspan 124. VCSEL 400 can further comprise an appropriate mode selectivitystructure 446, such as a dielectric mirror or mode control structure aspreviously described.

FIG. 5 provides an illustration of the current flow of VCSEL 400.Indicators 500 depict operational current flow of VCSEL 400. The currentdensity is maximized in the center portion 502 of VCSEL 400, coincidingwith the peak of the lowest order mode. Current coinciding with higherorder modes is widely dispersed, maximizing loss for those modes andeffectively damping all but the lowest order mode. As previously taught,the present invention thus provides a single mode (i.e. the lowest ordermode) VCSEL device, operational over a wide current range.

The embodiments and examples set forth herein are presented to bestexplain the present invention and its practical application and tothereby enable those skilled in the art to make and utilize theinvention. Those skilled in the art, however, will recognize that theforegoing description and examples have been presented for the purposeof illustration and example only. The teachings and concepts of thepresent invention can be applied to other types of components, packagesand structures, such as VCSEL components produced with other than a(100) orientation. The invention is applicable independent of aparticular package configuration. Other variations and modifications ofthe present invention will be apparent to those of skill in the art, andit is the intent of the appended claims that such variations andmodifications be covered. The description as set forth is not intendedto be exhaustive or to limit the scope of the invention. Manymodifications and variations are possible in light of the above teachingwithout departing from the spirit and scope of the following claims. Itis contemplated that the use of the present invention can involvecomponents having different characteristics. It is intended that thescope of the present invention be defined by the claims appended hereto,giving full cognizance to equivalents in all respects.

1. An optoelectronic device, comprising: a first mirror; a secondmirror; one or more heat conduction layers formed between the firstmirror and the second mirror, at least one of the heat conduction layersbeing periodically doped to maximize doping at minima of electric fieldsin the optoelectronic device; an active region situated between thefirst mirror and the second mirror; an insulating layer positioned in oradjacent to the first mirror, the insulating layer defining an aperture;and an isolation implant region extending around, and spaced outwardlyfrom, at least part of the aperture of the insulating layer andtraversing through the insulating layer and at least part of the firstmirror.
 2. An optoelectronic device according to claim 1 wherein theisolation implant region also traverses through the active region.
 3. Anoptoelectronic device according to claim 2 wherein the isolation implantregion traversed through the active region and at least partially intothe second mirror.
 4. An optoelectronic device according to claim 1wherein the isolation implant region extends entirely around theperimeter of the aperture of the insulating layer.
 5. An optoelectronicdevice according to claim 1 wherein the isolation implant region definesan aperture that is larger than the aperture of the insulating layer. 6.An optoelectronic device according to claim 5 wherein the aperture ofthe isolation implant region is substantially coaxial with the apertureof the insulating layer.
 7. An optoelectronic device according to claim1, wherein the first mirror comprises: a first DBR layer that hassubstantially isotropic conductivity; a second DBR layer including theinsulating layer, the second DBR layer having a doping level to minimizeseries resistance and heating effects in the aperture; and a third DBRlayer formed over the second DBR layer.
 8. An optoelectronic deviceaccording to claim 1 wherein the optoelectronic device is a VerticalCavity Surface Emitting Laser (VCSEL).
 9. A method for forming anoptoelectronic device, the method comprising the steps of: providing alower mirror; providing an active region above the lower mirror;providing a first DBR layer in an upper mirror above the active region,the first DBR layer having a first doping level; providing a second DBRlayer in the upper mirror, the second DBR layer including an insulatinglayer that defines an aperture, the second DBR layer further having asecond doping level that is higher than the first doping level;providing an isolation implant in an implant region, wherein the implantregion extends around, and is spaced outwardly from, at least part ofthe aperture of the insulating layer and traverses down through at leastpart of the upper mirror and through the insulating layer; providing athird DBR layer formed above the second DBR layer; and providing one ormore conduction layers formed between the lower mirror and the uppermirror, the one or more conduction layers being periodically doped suchthat heavy doping occurs at nulls of an electric field in theoptoelectronic device.
 10. An optoelectronic device A method accordingto claim 9 wherein the isolation implant region traverses through theactive region.
 11. A method according to claim 10 wherein the isolationimplant region traverses through the active region and at leastpartially into the lower mirror.
 12. A method according to claim 9wherein the isolation implant region extends entirely around theperimeter of the aperture of the insulating layer.
 13. A methodaccording to claim 9 wherein the isolation implant region defines anaperture that is larger than the aperture of the insulating layer.
 14. Amethod according to claim 13 wherein the aperture of the isolationimplant region is substantially coaxial with the aperture of theinsulating layer.
 15. A method according to claim 9 wherein theisolation implant region is implanted with protons.
 16. A methodaccording to claim 9 wherein the optoelectronic device is a VerticalCavity Surface Emitting Laser (VCSEL).